READV(3)

NAME
readv, writev - read or write data into multiple buffers

SYNOPSIS
#include <sys/uio.h>

int readv(int filedes, const struct iovec *vector,
          size_t count);

int writev(int filedes, const struct iovec *vector,
          size_t count);

DESCRIPTION
The readv() function reads count blocks from the file associated with the file descriptor filedes into the multiple buffers described by vector.

The writev() function writes at most count blocks described by vector to the file associated with the file descriptor filedes.

The pointer vector points to a struct iovec defined in <sys/uio.h> as

struct iovec {
void *iov_base;   /* Starting address */
size_t iov_len;   /* Number of bytes */
};

Buffers are processed in the order vector[0], vector[1], ... vector[count].

The readv() function works just like read(2) except that multiple buffers are filled.

The writev() function works just like write(2) except that multiple buffers are written out.

RETURN VALUES
The readv() function returns the number of bytes or -1 on error; the writev() function returns the number of bytes written.

ERRORS
The readv() and writev() functions can fail and set errno to the following values:

EBADF
    fd is not a valid file descriptor.

EINVAL
    fd is unsuitable for reading (for readv()) or writing (for writev()).

EFAULT
    buf is outside the processes' address space.

EAGAIN
    Non-blocking I/O had been selected in the open() call, and reading or writing could not be done immediately.

EINTR
    Reading or writing was interrupted before any data was transferred.

CONFORMING TO
unknown

BUGS
It is not advisable to mix calls to functions like readv() or writev(), which operate on file descriptors, with the functions from the stdio library; the results will be undefined and probably not what you want.

SEE ALSO
read(2), write(2)